The victim, from nearby Barnewall Gardens – originally from Finglas – was not known to gardai for involvement in organised crime, sources said.

He was pronounced dead at the Mater Hospital after the shooting at Gateway Avenue, Ballymun.

He was shot up to six times with a handgun by the lone gunman who fled the scene on foot.

Detectives are probing whether a dangerous Finglas gang are behind the murder as it is believed that Mr O'Regan got involved in a dispute with a senior member of this mob in recent times and felt under threat.

Despite a lack of criminal convictions, sources say that Mr O’Regan was under investigation after gardai seized a shotgun from him which was not licensed to him.

Window cleaning equipment was found near the scene of the capital's latest gun murder and it is understood that Mr O'Regan was on his way to do a job.

Local residents told The Herald that they heard six shots being fired in rapid succession and then heard a scream.

“I was in bed at the time and then I just heard six bangs, then someone screamed loudly. I don't know if it was the victim or a witness,” they said.

“When I looked out the window I could see garda and ambulance guys down on the ground with the victim,” he added.

Advanced paramedics from Dublin Fire Brigade tried to save the man's life but he was pronounced dead in the Mater Hospital after being rushed there. Local sources said a four-wheel-drive style vehicle was seen leaving the scene after the shooting.

The area where the attack occurred is a small cul de sac off the main Ballymun Road and is beside a school, which was closed today for the Easter Holidays.

The murder of Mr O'Regan is the second fatal shooting to happen in the morning rush hour in north Dublin in the space of just three weeks.

In an unrelated gun attack, IRA gangster Declan ‘Fat Deccy' Smith (31) was shot in the face outside a crèche in Donaghmede, north Dublin, shortly after 9am on March 21.

Smith died of his horrific injuries from the single shotgun wound in Beaumont Hospital a week later.

And last August, a 51-year old man survived after he was shot in the stomach as he cycled on Glasnevin Avenue in Ballymun in an incident that also occurred in the morning rush hour.

Sean Tyrell, an Independent election candidate for Dublin north west told The Herald this morning: “People that I have been talking to are in total shock, especially that this happened in an area that is normally quite busy at the time of the incident”

“There is a primary school right beside the scene, and a creche about 20-50 meters away”

“I'm just thankful that the kids are off on their Easter holidays”

“It's very unsettling for people to know that this can happen in their own back garden.”

“Even though the Garda station is across the road from the scene of the incident, they simply do not have enough resources, and they do the best job that they can, so I would encourage anybody with information to contact them,” he said.